I’ve been building a cabling solution to make a basic IEM (in-ear monitor) system for work, and have had the opportunity to do some critical listening of our chosen headphone amplifier, the discontinued Samson S-Monitor.

It’s a simple device: feed it power from its wall-wart PSU, then feed it a stereo signal to its ‘mix’ input via the unbalanced stereo 6.5mm jack on the back. It can also receive a dynamic microphone input on balanced XLR. Each input has its own level control, which feeds a fixed-level amplifier which can power its two headphone outputs, both on conventional 6.5mm unbalanced jack sockets. I’d prefer for one of these to be a 3.5mm socket so that earbud/canal earphones can be used without an adaptor.

For the experiment I’ve plugged the unit into my EMU 0202 USB, fed from a Linux laptop providing audio from ripped CD’s, upsampled in real-time to 176.4KHz 24-bit.

Compared with the headphone output of my usual hifi amplifier, a NAD 3020B, all headphones have sounded smoother and more controlled when fed by the Samson, with less grain and what feels like a more linear, more dynamic sound at all playback levels.

Used with Sennheiser HD25SP’s, their sound becomes brighter, with wider soundstaging and less of a sense of being ‘closed in’ to my own head.

With Shure SE110 canal earphones, their sound is both brighter in the treble range, with more bass being allowed through and more dynamic range, especially on percussive instruments.

For a laugh, I also tried the earbuds bundled with my iPhone, which took on a much better top-end than when used with the iPhone or the hifi, but became over-warm in low-mids. That said, they did have better control of low bass notes, and seemed to play an octave lower than I’m used to.

All in, i’m surprised at how good this cheap little device sounds! I’ve yet to make it distort before either my eardrums or the headphone drivers give out – which suggests a good amount of headroom and good current delivery.

The only downside seems to be that it’s more sensitive to mobile phone interference than i’d like – If the headphone cable runs against a phone in a pocket, some interference gets through. I couldn’t make it pick up interference when holding an phone to the power cable or the audio input cables.